This invention relates to using an insulin-like growth factor-I to prevent or treat peripheral neuropathy.
Insulin like growth factor-I (IGF-I; somatomedin C) is a member of a family of structurally and functionally related polypeptides which also includes insulin, and insulin like growth factors II (IGF-II) and III (IGF-III). All of these protein factors may play a role in neuronal development and maintenance (Recio-Pinto, E., et al., 1988, Neurochem. Int. 12:397-414). In addition, there is evidence that the levels of IGF-I and IGF-II increase substantially during regeneration after sciatic nerve transection (Hansson, H. A., et al., 1986, Acta Physiol. Scand., 126:609-614). They have been shown to promote the survival of cultured sensory and sympathetic neurons (Ishii, D. N., et al., 1987, In: Insulin, IGFs and Their Receptors in the Central Nervous System, eds., Raizada, M. K., et al., Plenum Press, N.Y., pp. 315-348) and, in the case of IGF-I, to promote the survival of cortical neurons (Aizenman, Y., et al., 1987, Brain Res., 406:32-42). Finally, studies both in-vitro and in-vivo have demonstrated that IGF-I and IGF-II promote motor neuron survival and neurite outgrowth (Caroni, P., et al., 1990, J. Cell Biol., 110:1307-1317).
Peripheral neuropathy generally refers to a disorder that affects the peripheral nerves, most often manifested as one or a combination of motor, sensory, sensorimotor, or autonomic neural dysfunction. The wide variety of morphologies exhibited by peripheral neuropathies can each be uniquely attributed to an equally wide variety of causes. For instance, peripheral neuropathies can be genetically acquired, can result from a systemic disease, or can be induced by a toxic agent. Some toxic agents that cause neurotoxicities are therapeutic drugs, antineoplastic agents, contaminants in foods or medicinals, and environmental and industrial pollutants.
In particular, chemotherapeutic agents known to cause sensory and/or motor neuropathies include vincristine, an antineoplastic drug used to treat haematological malignancies and sarcomas. The neurotoxicity is dose-related, and exhibits as reduced intestinal motility and peripheral neuropathy, especially in the distal muscles of the hands and feet, postural hypotension, and atony of the urinary bladder. Similar problems have been documented with taxol and cisplatin (Mollman, J. E., 1990, New Eng Jour Med. 322:126-127), although cisplatin-related neurotoxicity can be alleviated with nerve growth factor (NGF) (Apfel, S. C. et al., 1992, Annals of Neurology 31:76-80). Although the neurotoxicity is sometimes reversible after removal of the neurotoxic agent, recovery can be a very slow process (Legha, S., 1986, Medical Toxicology 1:421-427; Olesen, et al., 1991, Drug Safety 6:302-314).
There are a number of inherited peripheral neuropathies, including: Refsum's disease, Abetalipoproteinemia, Tangier disease, Krabbe's disease, Metachromatic leukodystrophy, Fabry's disease, Dejerine-Sottas syndrome, and others. Of all the inherited neuropathies, the most common by far is Charcot-Marie-Tooth Disease.
Charcot-Marie-Tooth (CMT) Disease (also known as Peroneal Muscular Atrophy, or Hereditary Motor Sensory Neuropathy (HMSN)) is the most common hereditary neurological disorder. It is characterized by weakness and atrophy, primarily of the peroneal muscles, due to segmental demyelination of peripheral nerves and associated degeneration of axons and anterior horn cells. Autosomal dominant inheritance is usual, and associated degenerative CNS disorders, such as Friedreich's ataxia, are common.
There are two primary forms of CMT Disease. Type I (70% of cases) was believed to have demyelination as its initial pathophysiology, but distal clinical involvement suggests a primary axonal degeneration, as in Type II. Type II (30% of cases) is primarily an axonal degeneration without demyelination, and may not be as severe as Type I. Nerve conduction impairment is often present at birth, though this is not a predictor of the possible age of onset or severity of progression. There are also very rare, Type III and Type IV forms, which are recessively-linked.